Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

712
FXUS63 KLOT 121123
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
623 AM CDT Sun Jul 12 2026

.KEY MESSAGES...

- Hot and humid conditions are expected for much of the upcoming
  week; cooler near Lake Michigan.

&&

.DISCUSSION...
Issued at 200 AM CDT Sun Jul 12 2026

Cirrus clouds seen on nighttime microphysics satellite imagery over
the southeastern part of the CWA are slowly drifting southward
and diminishing as an upper level trough continues to sink
toward the Gulf. Clearer skies and sunny conditions are expected
today as an upper level ridge over the Plains slides east. High
temperatures are expected to nudge into the mid to upper 80s
for most of the area this afternoon. Slightly cooler conditions
are expected near the lake with a lake breeze. But given models
projecting fairly weak lake breeze, temperatures could still
climb into the low 80s along the shore.

The upper level ridge is expected to amplify and park itself
over the Twin Cities tomorrow. 850 mb temperatures are expected
to exceed 20C for the early part of the week leading to
temperatures in the upper 80s and mid 90s at the surface
through at least Wednesday. There are two bits of uncertainty
with the upcoming heat wave: 1.) the longevity (more on that in
the next paragraph) and 2.) dew point temperatures. Models have
been struggling to agree on how much dew points will increase
and/or how well they will mix out during the afternoon. Given
the model spread, there is lower confidence with how things will
shake out, but as noted in yesterday`s afternoon discussion, it
is getting into that time of year where better evapotranspiration
is observed across the region. This forecast keeps the higher
dew point trend into the mid 70s during the early part of the
week. With highs in the 90s and dew points in the mid 70s, heat
index values can be expected in the upper 90s to at times around
100, especially on Tuesday which is currently projected to be
the hottest day of the week. Given the uncertainty and that it
is still days away, no consideration for a Heat Advisory was
given.

The weather pattern beyond Wednesday shows the ridge eventually
breaking down, but there is a lot of model spread in how and
when. An upper level low, currently over British Columbia, is
projected to be shunted over the dominating Plains upper level
ridge, but then descend down the east side of it mid week,
deepening as it crosses over Hudson Bay and into northern
Quebec. There is a chance that that low sends a reflective
surface cold front southward overnight Wednesday into Thursday
which may help mute temperatures ever so slightly. Beyond that,
the GFS and the Canadian models show the ridge weakening, but
generally remaining in place, whereas the Euro shows another
upper level trough developing and passing farther south over the
Great Lakes. Regardless, as the ridge breaks down any northwest
flow opens the door to a potential wave to descend near the
area and provide some chance for showers/storms over the
weekend.

DK

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 623 AM CDT Sun Jul 12 2026

Northeast winds around 10 kts will prevail today before
becoming light/variable tonight. VFR conditions expected.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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